Union officials said they could complain to Ofsted and the Department for Education over the "spiralling situation" at a city primary school.
Staff at Uplands Junior School, in Highfields, lodged a grievance with Leicester City Council in March against head teacher Tim Luckcock and chairman of governors Abid Matak.
The grievance outlines a number of concerns over the running of the school and proposals to axe several teaching assistants at the end of the summer term.
An independent investigation into the matter is yet to get underway, with union bosses urging the council to suspend Mr Luckcock while it takes place.
They say that a number of staff have taken sick leave because of stress and several have resigned because of the deteriorating situation.
Gary Garner, Leicester Unison branch secretary, said: "I'm aware a number of staff are now off sick due to stress they have been put under.
"We're now considering speaking to Ofsted and the Department for Education over the local authority's failure in its duty of care towards them as the situation is spiralling out of control.
"They are under a huge amount of strain while the head is still in his position."
Staff from the National Union of Teachers (NUT) went on strike last month and on Tuesday this week to lobby against the redundancies.
Another day's strike is planned today, forcing the school to shut. Parents were informed by letter last night.
Ian Leaver, assistant secretary for the Leicester branch of the NUT, said: "It's difficult to see how any investigation can take place with the head teacher still there, as it places staff under enormous strain.
"We're not happy with the local authority for handling it in this way and are still hopeful that Mr Luckcock's suspension will be forthcoming."
Members of the ATL teaching union have balloted to strike and are expected to take action next Thursday.
Spokesman David Brierley said: "Our action follows deep concern about the entire situation over redundancies and the grievance in general. It's most unusual to have the head teacher remain in place given what's happened."
A council spokesman said: "The investigation has not yet started as there are still some issues to be resolved, however, the unions will be discussing our proposals with their members today."
Mr Luckcock was not available for comment yesterday.
Mr Matak said: "The governing body has been trying to begin an independent investigation for a number of weeks and since making the proposal has spent time with the local authority and made efforts with the unions in order to get buy in from the parties.
"In order to resolve the issues and prevent further disruption, the governing body is taking all steps it can while acting in the best interests of the school and the children in it."
